I. Field
The present disclosure relates generally to electronics, and more specifically to techniques for attenuating undesired signal components from a duplexer in a wireless communication device.
II. Background
A wireless communication device (e.g., a cellular phone) may have a transmitter and a receiver to support two-way radio communication with a wireless communication system. For data transmission, the transmitter may modulate a radio frequency (RF) carrier signal with data to obtain a modulated signal. The transmitter may further filter and amplify the modulated signal to obtain a transmit signal and may then transmit this signal via a wireless channel to base stations in the wireless system. For data reception, the receiver may receive signals from base stations and may process a received signal to recover data sent by the base stations to the wireless device.
The wireless system may utilize frequency division duplexing (FDD). With FDD, one frequency channel is used for the forward link (or downlink) from the base stations to the wireless device, and another frequency channel is used for the reverse link (or uplink) from the wireless device to the base stations. The wireless device may be able to simultaneously transmit and receive data on the two frequency channels. The wireless device may have a duplexer to route an RF input signal from an antenna to the receiver and to route the transmit signal from the transmitter to the antenna. The duplexer provides isolation between the transmitter and the receiver sharing the same antenna. Ideally, the duplexer should not couple any of the transmit signals to the receiver. In practice, the duplexer may not have good isolation between a transmit port and a receive port, and a relatively large amount of the transmit signal may be coupled to the receiver. The coupled transmit signal may degrade the performance of the receiver or may even cause the receiver to fail specifications.